Gate-length dependence of the speed of SSI circuits using submicrometer selectively doped heterostructure transistor technology

Frequency dividers and ring oscillators have been fabricated with submicrometer gates on selectively doped AIGaAs/GaAs heterostructure wafers. A divide-by-two frequency divider operated up to 9.15 GHz at room temperature, dissipating 25 mW for the whole circuit at a bias voltage of 1.6 V, with gate length ∼ 0.35 µm. A record propagation delay of 5.8 ps/gate was measured for a 0.35-µm gate 19- stage ring oscillator at 77 K, with a power of 1.76 mW/gate, and a bias voltage of 0.88 V. The maximum switching speed at room temperature was 10.2 ps/gate at 1.03 mW/gate and 0.8 V bias, for a ring oscillator with the same gate length. With a range of gate lengths on the same wafer fabricated by electron-beam lithography, a clear demonstration of gate-length dependence on the propagation delay was observed for both dividers and ring oscillators.